Modern computer networks can include various types of storage servers. Storage servers can be used for many different purposes, such as to provide multiple users with access to shared data or to back up mission-critical data. A file server is a type of storage server which operates on behalf of one or more clients to store and manage shared files in a set of mass storage devices, such as magnetic or optical storage based disks or tapes. The mass storage devices are typically organized into one or more volumes of Redundant Array of Independent (or Inexpensive) Disks (RAID). A single physical file server may implement multiple independent file systems, sometimes referred to as “virtual filers”.
One configuration in which a file server can be used is a network attached storage (NAS) configuration. In a NAS configuration, a file server can be implemented in the form of an appliance, called a filer, that attaches to a network, such as a local area network (LAN) or a corporate intranet. An example of such an appliance is any of the Filer products made by Network Appliance, Inc. in Sunnyvale, Calif.
A storage server can also be employed in a storage area network (SAN). A SAN is a highly efficient network of interconnected, shared storage devices. In a SAN, the storage server (which may be an appliance) provides a remote host with block-level access to stored data, whereas in a NAS configuration, the storage server provides clients with file-level access to stored data. Some storage servers, such as certain Filers from Network Appliance, Inc. are capable of operating in either a NAS mode or a SAN mode, or even both modes at the same time. Such dual-use devices are sometimes referred to as “unified storage” devices. A storage server such as this may use any of various protocols to store and provide data, such as Network File System (NFS), Common Internet File system (CIFS), Internet SCSI (ISCSI), and/or Fibre Channel Protocol (FCP).
A storage server may use any of various protocols to communicate with its clients, such as Network File System (NFS) and/or Common Internet File system (CIFS). The use of CIFS “shares” allows an advertised resource (e.g., one or more files or a portion thereof) to be moved to a new location on a file server. The client does not have to be informed that the resource has moved, and no state has to change on the client. Hence, if a virtual filer is moved from one location to a new one, it is not necessary to visit each and every client to make changes to the imported resources.
NFS exports, however, as used by the commonly deployed versions of the NFS protocol, NFS versions 2 and 3, do not allow for the moving of an advertised resource to a new location on a file server. Clients must be informed that the resource has been moved, and state must be changed on the client. Consequently, when a virtual filer is moved to a new location, it is necessary to visit each and every client to make changes to the imported resources.